A self-tightening chuck has, according my earlier patent application Ser. No. 08/225,525 filed 11, Apr. 1994, now U.S. Pat. No. 5,435,578, a chuck body centered on an axis and adapted to be rotated thereabout, a plurality of jaws radially displaceable on the body, and an adjustment sleeve rotatable on the body, formed with radially inwardly directed teeth, and engaged with the jaws such that rotation of the adjustment sleeve on the body in a forward direction displaces the jaws radially inward on the body and opposite rotation in a reverse direction displaces the jaws radially outward. A tightening ring rotatable on the body has stop formations for limiting its rotation on the body to a predetermined angular travel and a tightening spring braced angularly between the tightening ring and the body urges the tightening ring angularly in the forward direction. A locking body radially displaceable on the tightening ring is formed with teeth meshable with teeth of the tightening ring. A locking spring braced radially against the locking body urges the locking-body teeth into mesh with the adjustment-sleeve teeth. The locking-body and adjustment-sleeve teeth are angled such that they lock together and rotationally couple the locking body and tightening ring to the adjustment sleeve on forward rotation of the tightening ring relative to the adjustment sleeve but slide past each other on forward rotation of the adjustment sleeve relative to the tightening ring. A locking ring angularly displaceable on the chuck body has a formation engageable with the body and displaceable between an unlocked position displacing the locking body radially inward out of engagement with the adjustment sleeve and a locked position leaving the locking body pressed radially by its locking spring against the adjustment sleeve. Stop formations engageable with the locking ring limit angular travel of the locking ring on the chuck body to an angular travel that is greater than the angular travel of the tightening ring on the chuck body.
The chuck according to this earlier invention is operated by gripping the locking ring in one hand and the adjustment sleeve in the other and relatively twisting them in the forward closing or backward opening direction, depending on what is wanted. As the adjustment ring is turned backward to open the chuck it first entrains the tightening ring backward against the force of the locking spring to pivot it relative to the locking ring, effectively moving the locking ring into the unlocked position so that further backward rotation retracts the jaws. Forward rotation similarly first moves the locking ring into the locked position and thereafter advances the jaws, with ratcheting of the adjustment-body teeth on the locking-body teeth. Such operation is intuitive and involves no careful gripping and/or manipulation of, for instance, the tightening ring. On tightening the forward torque is applied directly to the adjustment sleeve so that the chuck can be made very tight. Once tightened, the tightening spring will be loaded to rotate the adjustment sleeve forward if the chuck loosens.
A problem with this known chuck is that during drilling, in particular hammer drilling which subjects the chuck to considerable dynamic forces in every direction, the locking- and tightening-body teeth can be knocked out of engagement with each other. This allows the chuck to loosen, releasing the bit engaged in its jaws. Such disengagement is possible when teeth formed at the free end of an arm on the locking body vibrate out of engagement with the teeth of the tightening body, even though this arm is being biased outward by engagement near its base.